It is highly recommended to recite Azan and more importantly Iqama for daily obligatory Prayers, but it is not obligatory. You can start you Prayer with out Azan and Iqama but you will be losing great deal of reward. Hadeeth states that if you recite Azan and Iqama and start your Salah, two rows of angles will pray behind you. If you recite Iqama then start your Salah, one row of angles will pray behind you. If you don't recite neither Azan nor Iqama and pray, you will pray alone then. Your prayer will still be valid but you will be losing great deal of reward.
Wassalam.